Adapting microelectronic packages to micro electro-mechanical system (MEMS) devices involves several challenging packaging requirements. The typical three-dimensional and moving elements of many MEMS devices generally require some sort of cavity package to provide free space above the active surface of the MEMS device. The interior of the cavity must generally be free of contaminants, including excessive outgassing of materials. The MEMS device might also require thermal isolation within the package, and a mounting method that minimizes mechanical stress on the device. The cavity may be evacuated or be filled with atmosphere-controlling agents such as getters.
In addition to these requirements, MEMS devices are vulnerable to damage during what would otherwise be normal micropackaging procedures. The presence of three-dimensional mechanical structures that can move adds fragility to unpackaged MEMS devices. For example, movable MEMS structures make contact and permanently stick together (stiction effect) if roughly handled.
Further, the cost of MEMS packaging has become a critical issue for many applications. For instance, 50-90% of the cost in producing most MEMS devices is spent in packaging the MEMS devices. For instance, the surface features and cavity requirements of MEMS devices typically prohibit application of low-cost transfer-molded plastic packaging used for most integrated circuits. Moreover, common encapsulation techniques such as injection molding, often require high pressures that may easily damage microstructures.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.